1. Field of the Invention
The present invention relates to a rotation-preventive device and an electric actuator having a rotation-preventive function which make it possible to prevent, for example, a spline shaft from rotation in the circumferential direction by means of engagement of the spline shaft with a hole of a boss.
2. Discussion of the Background
For example, a spline has been hitherto used to prevent a shaft member from rotation in the circumferential direction. As shown in FIG. 23, the spline 1 includes a spline shaft 4 which has a plurality of teeth 3a to 3h having a substantially trapezoidal cross section formed in the circumferential direction along the outer circumferential surface between adjoining grooves 2a to 2h separated from each other by a predetermined angle, and a boss 6 which is provided relatively slidably in the axial direction of the spline shaft 4 and which is formed with a hole 5 having a shape corresponding to the cross-sectional shape of the spline shaft 4 in a direction perpendicular to the axis.
In this case, as shown in FIG. 24, a predetermined clearance A is formed between the teeth 3a to 3h of the spline shaft 4 in the circumferential direction and the inner wall surface of the hole 5 of the boss 6 corresponding to the teeth 3a to 3h. The clearance A is formed as follows. That is, the spline shaft 4 is formed, for example, by means of the thread rolling. The boss 6 is formed, for example, by means of the drawing. After that, the finishing machining is applied to the teeth 3a to 3h of the spline shaft 4 and the inner wall surface of the hole 5 of the boss 6.
However, the spline 1 concerning the conventional technique as described above involves the following inconvenience. That is, the clearance A is dispersed due to an error occurring in machining accuracy. Further, the teeth 3a to 3h of the spline shaft 4 are abraded due to the sliding friction with respect to the inner wall surface of the hole 5 of the boss 6, and the clearance A is increased so as to be larger than a preset predetermined value. As a result, backlash is caused when the spline shaft 4 and the boss 6 make the relative sliding displacement in the axial direction.
An electric actuator 10 has been hitherto used as a means for transporting a workpiece. As shown in FIG. 25, the electric actuator 10 comprises a motor 14 which is arranged at one end of a body 12 of the electric actuator 10, and a feed screw 18 which is coupled to a rotary shaft of the motor 14 and which is inserted into a hole 16 of the body 12. A feed nut 20 is meshed with the feed screw 18. The feed nut 20 is secured to one end of a cylindrical member 22. The other end of the cylindrical member 22 is secured to a movable member 24. A guide block 26 is secured to the movable member 24. The guide block 26 is slidably engaged with a guide rail 28.
When the motor 14 is energized in the electric actuator 10, then the feed screw 18 is rotated to move the feed nut 20 in the axial direction of the feed screw 18, and the movable member 24, which is secured to the cylindrical member 22, is linearly displaced. In the electric actuator 10, the guide block 26, which is coupled to the movable member 24, slides along the guide rail 28 which is provided at the outside of the body 12. Thus, the rotation-preventive function is effected to prevent the movable member 24 from rotation together with the feed screw 18.
An electric actuator 30 concerning another conventional technique is shown in FIG. 26. The electric actuator 30 comprises a movable member 32 which is secured to one end of a cylindrical member 22. One end of a guide shaft 34 is secured to the movable member 32 in parallel to the cylindrical member 22. On the other hand, an end plate 36 is secured to one end of a body 12. A bush 38 for inserting the guide shaft 34 therethrough is provided in the end plate 36.
In the electric actuator 30, the guide shaft 34 is guided by the bush 38. Accordingly, the rotation-preventive function is effected to prevent the movable member 32 from rotation together with the feed screw 18.
However, the electric actuators 10, 30 involve the following drawback. That is, the rotation-preventive mechanism for preventing the movable member 24, 32 from rotation is provided at the outside of the body 12. Therefore, the entire shape of the electric actuator 10, 30 becomes large.
In order to realize a compact size, it is conceived that the rotation-preventive mechanism for preventing the movable member from rotation is provided at an inside portion of the body of the electric actuator. For example, as shown in FIG. 27, a ring-shaped guide member 42 is secured to one end of a cylindrical member 22 of an electric actuator 40. A groove 44 is defined on the guide member 42 so that the groove 44 is parallel to the axis of the cylindrical member 22. On the other hand, a rail section 48, with which the groove 44 is slidably engaged, is formed on the wall of a hole 46 of the body 12. When the groove 44 of the guide member 42 makes sliding movement along the rail section 48, the rotation-preventive function is effected to prevent the cylindrical member 22 from rotation.
An electric actuator 50 concerning still another conventional technique is shown in FIG. 28. In the electric actuator 50, a guide member 54, which is formed with a spline 52, is secured to one end of a cylindrical member 22. A spline groove 58, with which the spline 52 is slidably engaged, is formed on the inner wall of a hole 56 defined in a body 12. In the electric actuator 50, the engagement between the spline 52 and the spline groove 58 effects the rotation-preventive function to prevent the cylindrical member 22 from rotation.
An electric actuator 60 concerning still another conventional technique is shown in FIG. 29. The electric actuator 60 comprises a spline 64 which is formed over the entire outer circumference of a lengthy cylindrical member 62. An end plate 66 is secured to an end of a body 12. A spline groove 68, with which the spline 64 is slidably engaged, is formed on the end plate 66. In the electric actuator 60, the engagement between the spline 64 and the spline groove 68 effects the rotation-preventive function to prevent the cylindrical member 62 from rotation.
However, the electric actuators 40, 50, 60, each of which is provided with the rotation-preventive mechanism at the inside of the body 12, require the exclusive part having the specified structure as the rotation-preventive mechanism to prevent the cylindrical member 22, 62 from rotation, including, for example, the guide member 42 formed with the groove 44, the guide member 54 with the spline 52 formed on the outer circumferential surface, and the cylindrical member 62 formed with the spline 64. Therefore, a problem arises in that the production cost of the electric actuators 40, 50, 60 is expensive.
An object of the present invention is to provide a rotation-preventive device which makes it possible to conveniently and freely adjust the clearance in the circumferential direction between teeth of a spline shaft and an inner wall surface of a hole of a boss.
Another object of the present invention is to provide an electric actuator having a rotation-preventive function which makes it possible to reduce the production cost by using parts hitherto used generally so that any exclusive part is unnecessary.
According to the present invention, a first spline shaft member and a second spline shaft member, which are divided into two, are rotated and displaced in mutually opposite directions about a center of rotation of the axis. Thus, it is possible to freely adjust the clearance in the circumferential direction between an inner wall surface of a boss section and an outer wall surface of a spline shaft section.
Further, a first boss member and a second boss member, which are divided into two, are rotated and displaced in mutually opposite directions about a center of rotation of the axis. Thus, it is possible to freely adjust the clearance in the circumferential direction between an inner wall surface of a boss section and an outer wall surface of a spline shaft section.
According to another aspect of the present invention, a guide rail and a guide block, which have been used as guide means in the conventional technique, are allowed to simultaneously possess the rotation-preventive function. Thus, a displacement member of an electric actuator is prevented from rotation.
In this arrangement, it is preferable that a plurality sets of the guide rails and the guide blocks are provided. By doing so, when a large radial load is applied to a cylindrical member, the load can be supported by the plurality of guide rails and the plurality of guide blocks. Therefore, it is possible to transport a workpiece having a heavy weight, which is preferred.
It is also preferable that a plurality of guide blocks are slidably engaged with the guide rail in the longitudinal direction. By doing so, the radial load, which is applied to the displacement member, can be supported by the plurality of guide blocks in a stable manner. Therefore, it is possible to stably transport a workpiece, which is preferred.